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  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
  • C07K5/04—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing only normal peptide links
  • C07K5/06—Dipeptides
  • C07K5/06139—Dipeptides with the first amino acid being heterocyclic
  • C07K5/06165—Dipeptides with the first amino acid being heterocyclic and Pro-amino acid; Derivatives thereof
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/58—Preparation of carboxylic acid halides
  • C07C51/60—Preparation of carboxylic acid halides by conversion of carboxylic acids or their anhydrides or esters, lactones, salts into halides with the same carboxylic acid part
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  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D207/00—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom
  • C07D207/02—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D207/04—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having no double bonds between ring members or between ring members and non-ring members
  • C07D207/10—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having no double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D207/16—Carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D211/00—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings
  • C07D211/04—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D211/06—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having no double bonds between ring members or between ring members and non-ring members
  • C07D211/36—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having no double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D211/60—Carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D277/00—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings
  • C07D277/02—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings not condensed with other rings
  • C07D277/04—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings not condensed with other rings having no double bonds between ring members or between ring members and non-ring members
  • C07D277/06—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings not condensed with other rings having no double bonds between ring members or between ring members and non-ring members with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms

Definitions

• the product of the present invention inhibits the enzymatic conversion of angiotensin I into angiotensin II and therefore is useful for relieving angiotensin-related hypertension.
• Potency of N-mercaptoalkanoylamino acids such as N-(3-mercapto-2-D-methylpropanoyl)-L-proline which is considered the most prospective as a hypotensive drug, critically depends on the configuration of the mercaptoalkanoyl side chain of the compounds [M. A. Ondetti et al., Biochemistry, 16, 5484 (1977); The Medical Journal of Australia, Vol. 2, p. 1 et seq. "Symposium on Converting Enzyme Inhibition in Hypertension", (1979)].
• the compound specified above with L configuration in the mercaptoalkanoyl side chain is about 100 times less inhibitory against the enzyme than the corresponding D-enantiomer.
• the preparation of D-enantiomer of N-mercaptoalkanoylamino acids, for example, N-(3-mercapto-2-D-methylpropanoyl)-L-proline has thus far involved a troublesome optical resolution as an inevitable step because optically inactive starting materials have been used for their production [M. A. Ondetti et al., U.S. Pat. No. 4,046,889 (1977); U.S. Pat. No. 4,105,776 (1978); U.S. Pat. No. 4,154,840 (1979)].
• the known processes for their production include the reaction of an N- ⁇ -haloalkanoylamino acid with an anion of a thioacid such as thiolacetic acid or thiobenzoic acid in order to produce an N-acylthioalkanoylamino acid; therefore, the acyl group as a protecting group for the thiol group must finally be removed to obtain the desired N-mercaptoalkanoylamino acid.
• the object of the present invention is therefore to provide an improved process for preparing an optically active N-mercaptoalkanoylamino acid.
• the present inventors carried out researches in order to establish an improved process for preparing an optically active N-mercaptoalkanoylamino acid and have now completed the present invention.
• an optically active N-mercaptoalkanoylamino acid (I) can be obtained starting from an optically active ⁇ -hydroxyalkanoic acid (III) in a simple process which involves neither the step of optical resolution nor the step of protection of the thiol group as explained hereinbefore. It is an advantageous feature of the present invention that the configuration of all the optically active compounds involved in the process is retained throughout the process.
• the starting materials of the present invention have come to be produced industrially according to inventions by some of the present inventors in which the compound (III) is produced by subjecting the corresponding alkanoic acid to the stereospecific action of microorganisms.
• the compound (III) in which R 1 is methyl can be produced by subjecting isobutyric acid or methacrylic acid to the stereospecific action of specific microorganisms [Japanese patent applications Nos. 144252/1979, 144253/1979, 17559/1980, 103805/1980, 140258/1980, 140259/1980, and 141453/1980].
• the present invention is very advantageous in that the starting material is readily available industrially and the optical activity thereof can be retained to produce the desired optically active product.
• the present invention has eliminated the foregoing drawbacks of known processes, thus providing an advantageous process for preparing an optically active N-mercaptoalkanoylamino acids.
• optically active ⁇ -chlorophenylacetic acid was produced from mandelic acid according to a two-step process in which the carboxyl group was first protected by esterification with ethanol and then halogenation with thionyl chloride was conducted, the aimed free acid finally being obtained by hydrolysis of the ester group.
• halogenation of an optically active ⁇ -hydroxyalkanoic acid (III) can be performed on both the hydroxyl group and the carboxyl group in one step with retention of the configuration to produce an optically active ⁇ -haloalkanoyl halide (IV).
• the conversion of the halogen in the compound (VI) into the thiol group in the third step of the process of the present invention is conducted with the usual reagents capable of converting the halogen into the thiol group [P. Klason and T. Carlson, Chem. Ber., 39, 732 (1906); Fore a review of the reaction, see Methoden der Organischen Chemie (Houben-Weyl), Vol. 9, p. 7 et seq. (1955)].
• reagents capable of converting the halogen into the thiol group
• the reagent e.g., sodium hydrosulfide or ammonium hydrosulfide is strongly alkaline in solution and therefore no one has ever tried the application of the reagent to an optically active compound because racemization is expected to take place readily under such alkaline conditions.
• the lower alkyl groups having from 1 to 4 carbon atoms represented by R 1 in compounds (I), (III), (IV), and (VI) include straight and branched chain hydrocarbon groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, and so forth.
• Preferred compounds for medicinal uses among the compound (I) are those wherein R 1 is methyl and Y is CH 2 , and R 1 is methyl and Y is sulfur; especially preferred are those wherein R 1 is methyl, Y is CH 2 , and Q is hydroxy; R 1 is methyl, Y is CH 2 , and Q is residual part of an amino acid (II) wherein R 2 is benzyl; and R 1 is methyl, Y is sulfur, and Q is hydroxy.
• the residual part of an amino acid represented by formula (II) include residual parts of alanine, glycine, valine, leucine, isoleucine, and phenylalanine, preferably phenylalanine.
• the optically active ⁇ -hydroxyalkanoic acid (III) can readily be converted into the optically active ⁇ -haloalkanoyl halide (IV) with retention of the optical activity in a one-step reaction as described hereinbefore.
• this step in the process of the present invention is the first facile method for preparing an optically active ⁇ -haloalkanoyl halide from an optically active ⁇ -hydroxyalkanoic acid with retention of the optical activity in one step reaction.
• the halogenation of the optically active ⁇ -hydroxyalkanoic acid (III) is conducted preferably in the presence of a catalyst such as an organic amine, acid addition salt thereof, or acid amide.
• a catalyst such as an organic amine, acid addition salt thereof, or acid amide.
• the organic amine is used, for example, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, imidazole, piperidine, morpholine, pyridine, N,N-dimethylaniline, or N,N-diethylaniline.
• Imidazole is the most preferable among these.
• a hydrochloride, hydrobromide, sulfate, or phosphate is used as an acid addition salt of the organic amine.
• the acid amide is used, for example, formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N,N-dimethylacetamide, N-formylmorpholine, or N-formylpiperidine.
• the molar ratio of the catalyst to the ⁇ -hydroxyalkanoic acid (III) is from about 0.0001 to about 0.1, preferably from about 0.0001 to about 0.05.
• the halogenating reagent is, for example, thionyl chloride or thionyl bromide.
• the molar ratio of the halogenating reagent to the ⁇ -hydroxyalkanoic acid (III) is from about 2 to about 3, preferably from about 2 to about 2.2.
• the halogenation can be conducted without a solvent; however, the use of an inert organic solvent, such as diethyl ether, tetrahydrofuran, methylene chloride, ethylene dichloride, chloroform, carbon tetrachloride, benzene, and toluene, makes the reaction controllable.
• the temperature control is important to minimize side reactions and to retain the configuration of the starting ⁇ -hydroxyalkanoic acid (III).
• the reactants that is, the halogenating reagent and the compound (III)
• the temperature of the resulting reaction mixture is raised up to from about 30° C. to about 100° C., preferably to from about 70° C. to about 80° C. to complete the reaction.
• the mixing of the two reactants described above can be carried out by adding by drops either of the two reactants to the other.
• an optically active ⁇ -haloalkanoyl halide (IV) is subjected to a coupling reaction with an amino acid (V), yielding an optically active N- ⁇ -haloalkanoylamino acid (VI).
• This coupling reaction is effected in an alkaline medium, such as a dilute aqueous solution of an alkali metal hydroxide, alkali metal bicarbonate, or alkali metal carbonate solution at a low temperature, e.g., about from 0° C. to about 15° C.
• an optically active N- ⁇ -haloalkanoylamino acid (VI) is then subjected to a displacement reaction of the halogen atom by the thiol group, yielding the disired product of the present invention, an optically active N-mercaptoalkanoylamino acid (I).
• the reagent capable of converting the halogen into the thiol group is, for example, a salt of hydrogen sulfide with an alkali or alkaline earth metal, ammonia, or an organic base, preferably sodium hydrosulfide or ammonium hydrosulfide.
• the organic base includes methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, pyridine, piperidin, morpholine, and imidazole, and so forth. Methylamine is preferable among the organic bases.
• the displacement reaction of the halogen by the thiol group is carried out in water or in a polar aprotic solvent such as dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.
• the reagents, described above, which are capable of converting the halogen into the thiol group are all strongly alkaline in water or in the polar aprotic solvent, but neither the compound (VI) nor the compound (I) undergoes racemization in this reaction. This is noteworthy since an optically active compound generally undergoes racemization in an alkaline solution. Further, there have thus far been no reports on displacement of a halogen atom of an optically active compound by a salt of hydrogen sulfide.
• the compound (I), obtained in the foregoing final step of the process is very susceptible to oxidation and liable to be oxidized to give the disulfide represented by the following formula: ##STR10## wherein R 1 , Y, and Q are the same as defined above, which can be reverted to the thiol compound (I) with the usual reducing reagent, e.g., zinc powder in a dilute mineral acid, and sodium hydrosulfite.
• Another by-product of the final step of the process is the sulfide of the following formula: ##STR11## wherein R 1 , Y, and Q are the same as defined above, which can hardly be converted into the thiol compound (I).
• the side reactions can be averted by adopting the optimum molar ratio of the salt of hydrogen sulfide to the N- ⁇ -haloalkanoyl amino acid (VI).
• the optimum molar ratio is from about 2 to about 10, preferably from about 4 to about 6.
• the concentration of the salt of hydrogen sulfide in the reaction system is also an important factor in minimizing the amount of by-products.
• the optimum concentration is from about 5 wt% to about 10 wt%.
• the reaction in an inert gas atomsphere is effective in minimizing the amount of the disulfide described above.
• the reaction is carried out at a temperature of from about 30° C. to about 100° C., preferably from about 60° C. to about 90° C., under which conditions no racemization occurs.
• the ⁇ -hydroxyalkanoic acid of formula (III) is halogenated with thionyl halide, preferably thionyl chloride, in an anhydrous inert organic solvent, preferably methylene chloride or toluene, in the presence of a catalyst, preferably imidazole, of which the molar ratio to the acid of formula (III) is from about 0.0001 to about 0.05, keeping the temperature of the reaction mixture at not more than 25° C.
• ⁇ -haloalkanoyl halide of formula (IV) is then coupled with the amino acid of formula (V) by a conventional method in which the coupling is effected in an alkaline medium, e.g., a dilute solution of an alkali metal hydroxide at a low temperature, e.g., from about 0° C. to about 15° C., yielding the ⁇ -haloalkanoylamino acid of formula (VI).
• an alkaline medium e.g., a dilute solution of an alkali metal hydroxide at a low temperature, e.g., from about 0° C. to about 15° C.
• the product is reacted with a reagent capable of converting the halogen into the thiol group, preferably sodium hydrosulfide or ammonium hydrosulfide, of which the molar ratio to the ⁇ -haloalkanoylamino acid of formula (VI) is from about 4 to about 6, in water or a polar aprotic solvent, preferably in water, at a temperature of from about 60° C. to about 90° C. to produce the N-mercaptoalkanoylamino acid of formula (I).
• a reagent capable of converting the halogen into the thiol group preferably sodium hydrosulfide or ammonium hydrosulfide, of which the molar ratio to the ⁇ -haloalkanoylamino acid of formula (VI) is from about 4 to about 6, in water or a polar aprotic solvent, preferably in water, at a temperature of from about 60° C. to about 90° C. to produce the N-mercaptoal
• the reaction mixture was diluted with cold water (10 ml), adjusted to pH 1 with sulfuric acid, and treated with zinc powder (0.5 g) as reducing agent by stirring at room temperature for 4 hr under nitrogen atmosphere, whereby the by-produced disulfide (ca. 5 mole %) was reduced to N-(3-mercapto-2-D-methylpropanyl)-L-proline.
• Insoluble materials were filtered off from the reaction mixture and washed with fresh methanol. The filtrate, combined with the washings, was evaporated to remove the methanol. The residual aqueous solution was extracted with ethyl acetate (50 ml ⁇ 3).
• An aqueous solution of ammonium hydrosulfide was prepared by saturating 0.5 M ammonium hydroxide solution (100 ml) with hydrogen sulfide at room temperature.
• this solution was dissolved N-(3-chloro-2-D-methylpropanoyl)-L-proline (1.0 g).
• the resulting mixture was warmed with stirring at 90° C. for 16 hr, when no starting halide was detected on the NMR spectrum.
• the reaction mixture was worked up in the same manner as in Example 10, giving white crystals of the desired product, N-(3-mercapto-2-D-methylpropanoyl)-L-proline (0.85 g, 86%).
• the by-produced disulfide (102 mg, 10%) and sulfide (10 mg, 1%) were also isolated.
• N-(3-chloro-2-D-methylpropanoyl)-L-thiazolidine-4-carboxylic acid was obtained as white crystals. mp 113°-114° C. [ ⁇ ] D 25 -172.0° (C 1.0, MeOH).
• Anal. Calc'd for C 8 H 13 NO 3 S 2 C; 40.83, H; 5.57, N; 5.95, Found: C; 40.74, H; 5.53, N; 5.90.
• N-(3-mercapto-2-D-methylpropanoyl)-L-proline from 3-chloro-2-D-methylpropanoyl chloride.

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